480 THE ARTERIES 



by the anastomosis of the uitenial carotid with the internal carotid of the opposite side throufrh 

 tlie circle of Willis ; by the vertebral with the ojjposite vertebral ; by the inferior thyroid with 

 the superior thyroid ; by the deep cervical branch of the superior intercostal with the princeps 

 cervicis of the occipital ; by the superior thyroid, lingual, facial, occipital and temporal, with the 

 corresponding arteries of the opposite side, and by the ophthalmic with the angular. The anas- 

 tomosis between the deep cervical branch of the superior intercostal with the princeps cervicis of 

 the occipital is an important one and is situated deeply at the back of the ueck, aud is to be found 

 lying between the complexus and semi-spinalis colli muscles. 



THE EXTERNAL CAROTID ARTERY 



The external carotid artery, the smaller of the two branches mto which the 

 common carotid divides at the upper border of the thyroid cartilage, is distributed 

 to the anterior part of the neck, the face, and the side of the skull both soft parts 

 and bones, the integuments externally, and dura mater internally. It is develop- 

 mentally derived from the third aortic arch, and supplies the oral and post-oral 

 visceral branches. It is at first situated internal to the internal carotid ; 1 )Ut as it 

 ascends in the neck it forms a gentle curve, with its convexit}' forwards, and, 

 running slightly backwards as well as upwards, terminates opposite the neck of the 

 lower jaw just below the condyle, by dividing into the internal maxillary and 

 superficial temporal arteries. It here lies superficial to the internal carotid, from 

 which it is separated by a portion of the parotid gland. At its origin it is 

 overlapped by the anterior margin of the sterno-mastoid, and is covered by the 

 superficial fascia, platysma, and deep fascia. Higher up the neck it passes beneath 

 the stylo-hyoid muscle, the posterior belly of the digastric muscle, and the hypo- 

 glossal nerve; and, entering the parotid gland, is situated deeply in that structure 

 at its division into its terminal branches. It is separated from the internal carotid 

 artery posteriorly by the stylo-jiharyngeus and stylo-glossus muscles, the glosso- 

 pharyngeal nerve, the pharyngeal branch of the pneumogastric nerve, a portion of 

 the parotid gland, and the stylo-hyoid ligament; or, if the styloid process is alnior- 

 mally long, by that process itself. It measures about two and a half inches 

 (6"5 cm.). 



Relations (fig. 329). — In front, in addition to the skin, superficial fascia, 

 platysma, and deep fascia, it has the hypoglossal nerve, the lingual and facial 

 veins, the posterior belly of the digastricus and stylo-hyoid muscles, the temporo- 

 maxillary vein, the superior cervical lymphatic glands, branches of the facial nerve, 

 and the parotid gland. The sterno-mastoid also overlaps it in the natural state of 

 the parts. 



Behind, it is in relation with the internal carotid, from Avhich it is separated 

 by the stylo-glossus and stylo-pharyngeus muscles, the glosso-pharvngeal nerve, the 

 pharyngeal branch of the pneumogastric nerve, the stylo-hyoid ligament, and the 

 parotid gland. The superior laryngeal nerve crosses behind both the external and 

 internal carotid arteries. 



Internally, it is in relation with the hyoid bone, the pharyngeal wall, the ramus 

 of the jaw, the stylo-maxillary ligament Avhich sejiarates it from the submaxillary 

 gland, and the parotid gland. 



Externally, in the first part of its course, it is in contact with the internal 

 carotid artery. 



Chief Variations of the External Carotid Artery 



The variations of the external carotid artery are not of much surgical im]iortance. The 

 variations in its origin have been discussed under A'ariations of the Common Carotid. 



(A) It may be absent, the branches usually derived from it coming off from the upward 

 continuation of the common trunk. 



( B) It may run superficial to the stylo-hyoid muscle. 



(C) Its branches may come oflF irregularly; or maybe diminished or increased in number 

 either by two or more arising as a common stem, or by its giving origin to branches not usually 

 derived from it, as the sterno-mastoid branch of either the superior thyroid or occipital artery. 



(D) At times all its branches come off close together just above its origin. 



The branches of the external carotid are usuallv given off in the following 

 order, from below upwards: — 



